Here’s the background. The ACC Control Head does not work properly on my 1983 300D. BIG SURPRISE!!! If I disconnect the temperature amplifier control, my heat works great, I just have to adjust the blower speed by using the push buttons. I don’t mind at all. My air conditioner compressor will run continually unless I run the temperature wheel to max so I just put a switch in the power line so I can turn it on and off manually. Now, it is getting rather hot here in Georgia and I need my A/C to work. I trusted a Yahoo on ebay and bought a used ACC Control Head “that works just fine”. Yeah, in a parallel Universe! Anyway, I am pretty sure that if I can turn off the flow of hot water through the heater box inside the car, that my A/C will work just fine. The A/C does produce cold air, but the heater gets so hot that it blows very warm air. If I feel under the dash, I can feel COLD air coming from behind the glove box.

Finally a question, is there something I can unplug or disconnect that will stop the flow of hot water into the heater box, or will if hurt anything if I just put a shutoff valve in the hot water line right after the auxiliary water pump? I am also open to other ideas. I tried the soldering trick on the ACC but it didn’t seem to work.

I know it is sacrilege to some of ya’ll to not repair it properly, but I’d rather not waste any more money on iffy ACC control heads that may or may not work.

Thanks,

__________________
Wayne

the triumph of evil requires only that good men stand by and do nothing

13 Audi A3 TDI, the Wife's!
85 190D 5 speed, 195,000 miles
75 Triumph TR 6 w/Toyota 5 speed
2000 Ford F-250 powerstroke
03 Ml500, 109000

I believe that what you are seeking is the "monovalve". On my 82 300SD it is located next to the battery by the firewall in the area between the engine bay and the passenger compartment. It has a connector with two wires to it and a couple of heater hose connections. It is my understanding that cutting the current to it by removing the connector will stop the flow of coolant to the heater core. The "proper" fix for your issue may be to recrimp the connectors for the wires there, or replace the insert by removing the 4 screws on top and pulling the insert out and replacing. Mine would stick in either the full flow or no-flow positions. Just replaced it today and all is fine.

Andrew

Buying used climate control units is probably a waste of time, you never know if you will get a good one. I would try the monovalve first, because it's cheap. After messing with my pushbutton unit for a while, I just bought a rebuilt unit from these guys:

http://www.gdl-online.com/price6.html

I believe they will test yours first and tell you if it's working correctly or not.

Then you should try disconnecting power to your monovalve. That will vastly improve your level of understanding, especially if you do it on a hot day!!!

If I'm wrong, fine. I'm new to the Benz scene... And you should try disconnecting YOUR dinkishness. It will vastly improve your interpersonal relationships on any day regardless of the weather!!!

Andrew

Well, it's not a hot day here, but curiousity got the better of me and I figured "what the heck, I'll check it out." I went out and got it up to temp with the temp wheel set on max, the fan set on high and the heat roasting me out of the car. I popped the hood and disconnected the electrical connector to the monovalve and got back in. Hmmm, no heat out any of the vents!!! Got back out and reconnected the monovalve and got back in. Heat blasting out of the vents.




Andrew

Here is a quote from the '82 MB Electrical Troubleshooting Manual:
Regarding the 300SD Mono Heater Valve: "SHUTS OFF WATER WHEN ENERGIZED"

Can anyone else replicate libbybapa's results?

Or does your monovalve open to the full heat position when electrical power is removed?

I was about to comment also that removing the monovalve connector will, if the monovalve screen isn't torn badly, give heat, lots of heat if the pump is running, a little less if its off (even with the pump unplugged there is some coolant flow thru the heater, its just not nearly as much). So the test is defying the logical operation - I suggest running the test again. The Gr$#Frikiing monovalve works opposite to what you would think! power applied = shut

__________________
'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

That's interesting. Normally, if the heat is on and operating, there is enough residual heat in the heater core that you continue to get warm air for a couple of minutes even after the heater is turned off (as when selecting a cooler temp on the temp selector while in the EC mode.) Hmmm......

OK guys, I disconnected the connector to the monovalve and my A/C compressor would not turn on. Once I reconnected the monovalve connector, it started working again. Of course, my temperature control amp is still disconnected so I don't know if that had anything to do with it or not. I had a long day at work and don't have time to go back out and run through it again tonight, but tomorrow I will reconnect the temp control amp, then disconnect the monovalve to see if the compressor runs.

If we are having this much fun with our MB's, you got to wonder how the automatic A/C controls in "lesser" cars are going to perform in 20 years.

__________________
Wayne

the triumph of evil requires only that good men stand by and do nothing

13 Audi A3 TDI, the Wife's!
85 190D 5 speed, 195,000 miles
75 Triumph TR 6 w/Toyota 5 speed
2000 Ford F-250 powerstroke
03 Ml500, 109000

Lesser cars tend to have manual controls, which are much less problematic!!!

To solve your problem temporarily, I think I would just plug one of the heater hoses and leave everything else alone. Disconnecting the mono valve power is not the answer, so don't waste your time.

For Gits and Shiggles I tested it again with the same results. With my monovalve disconnected, no heat blew out the vents. With it connected vents blew very hot. The monovalve insert is brand new as of yesterday and the engine was running. I did not check to see if my a/c would work with the monovalve disconnected, but the heat sure didn't. The transition from hot to ambient air was not instantaneous, but certainly did not take minutes. The transition back to hot when I reconnected the monovalve was very fast. I could not believe that I was taking the time to check it again as I was quite certain of the previous results and quite frankly could not care less which way the monvalve opens and closes, as currently my climate control system is working as it should and that's what I care about.

Andrew